It is often desirable to modify or enhance the appearance of various types of substrates by obscuring the surface of such substrates, such as wood, plastic, metal, ceramic, gypsum board (i.e., drywall or sheetrock), paper, fiber, and other, which are used for many purposes, such as flooring, interior and exterior walls, ceilings, roofs, architectural trims, motor vehicle bodies, containers, casings, piping, etc. The ability of opaque aqueous coating formulations, such as paints, primers, mastic sealants, and other opaque coatings, to obscure the color, appearance or pattern of the surface of a substrate, to which it is applied to form an opaque dried film, is sometimes referred to as hiding power or tint strength. Various inorganic materials comprising metal cations are used to impart various characteristics to the dried films resulting from application of aqueous opaque coating formulations. For example, pigments are added to provide opaqueness, tint strength, and even colors, to the formulations and dried films. Extenders (also known as fillers), on the other hand, are generally used to adjust the hardness, rheological properties and other characteristics of the dried films formed from the aqueous opaque coating formulations. In most such formulations, the tint strength of the dried film resulting from application of such formulations is strongly dependent on the type and quality of inorganic material used. Different types of inorganic pigments impart different colors for the dried film. Examples of inorganic pigments include titanium dioxide (TiO2, white), zinc oxide (ZnO, white), cobalt(II) stannate (Co2SnO4, blue), cadmium selenide (CdSe, red), cadmium sulfide (CdS, yellow), calcium copper silicate (CaCuSi4O10, blue), and hydrated chromium(III) oxide (Cr2O3, green). Extenders (fillers) that may typically be used in opaque coating formulations include, for example, talc (Mg3Si4O10(OH)2), calcium carbonate (CaCO3), nepheline syenite (characterized as having a high ratio of (Na2O+K2O)/SiO2+(Na2O+K2O)/Al2O3), barium sulfate (BaSO4), hydrous kaolin (Al2Si2O5(OH)4), mullite (Al2SiO5), pyrophyllite (Al2Si4O10(OH)2), kyanite (Al2OSiO4), sillimanite (Al2SiO5), attapulgite ((Mg,Al)5Si8O20.4H2O), and mica, among many others. Use of the aforesaid inorganic materials in coating formulations results in the presence of one or more metal cations in the coating formulation, including, without limitation, Ca2+, Mg2+, Ba2+, Sr2+, V2+, Mn2+, Fe2+, Al3+, Zr2+, Co2+, Cd2+, Zn2+, TiO2+, Pb2+, Y3+, Pd2+, Ni2+, VO2+, Cu2+, Ga3+, Ti3+, Hg2+, Sc3+, Th4+, In3+, Fe3+, V3+ and combinations thereof.
Presently, for example, TiO2 is the predominant white inorganic pigment used in the paint industry due to its high refractive index and superior light scattering capabilities, which imparts whiteness, brightness, opacity, light scattering and light stability. TiO2 is often among the most expensive ingredients in a paint formulation and, therefore, there is significant interest in a technology that improves the effective utilization of TiO2 in aqueous coating compositions by reducing the required level of TiO2 while maintaining or improving opacity and other paint properties. One known way of accomplishing this is by employing TiO2 particles having an optimal average particle size and particle size distribution for scattering light. See, for example, U.S. Pat. No. 5,385,960, in which the optimal particle size and spacing are stated as 200 to 250 nanometers, and a few particle diameters, respectively.
Furthermore, it is well understood that when the constituent particles of the inorganic materials are agglomerated or aggregated, they provide less opacity and tint strength than when fully dispersed. Thus, another known way of improving the tint strength performance of paint containing inorganic materials is by dispersing the particles as well as possible in the paint formulation. One way of accomplishing this for TiO2 particles, for example, is to improve the mechanisms for latex polymer adsorption onto the surface of TiO2 particles, thereby forming composite particles. In this area, the development of a wide variety of functional latexes for promoting the formation of latex polymer-pigment composite particles with improved hiding efficiencies has been reported. Aqueous compositions containing carboxylic acids functional groups are, in general, ineffective at promoting adsorption of latex particles onto the surfaces of inorganic particles, and have been associated with poor paint properties including poor water resistance properties, reduced scrub resistance and undesirable viscosity drift.
Another route has been to use polymeric latex particles having at least one phosphate containing compound, to promote adsorption of the polymeric latex particles onto the TiO2 particles, as described in U.S Pat. No. 5,385,960 which discloses aqueous dispersions of such composite particles. U.S. Pat. No. 7,179,531 also discloses aqueous dispersions of composite particles containing TiO2, but here multistage polymer particles also containing dihydrogen phosphate functional groups are adsorbed to the TiO2 particles.
Although latexes containing phosphate functional groups have provided paints with improved hiding performance, this approach is associated with polymerization process complexities in addition, some phosphate-containing latex polymers are known to exhibit undesirable increase in viscosity due to aggregation as a result of the “bridging” of two TiO2 particles by a single polymeric latex particle.
More recently, it has been recognized that acrylic polymers having chelating functionality are useful for binding metal ions in various applications. For instance, U.S. Pat. No. 3,331,773 teaches preparation of water soluble polymers having chelating functionality which are useful as water treatment agents for inhibiting calcium and magnesium scale formation. These polymers are formed by grafting water soluble chelating monomers onto water soluble polymers having aliphatic polymeric backbones. Diethylenetriamine, ethylenediamine tetraacetic acid (EDTA), and other polyalkylene polyamine polyacetic acids are identified in U.S. Pat. No. 3,331,773 as examples suitable chelating monomers.
U.S. Pat. No. 5,426,142 teaches film-forming polymers which contain acetoacetate functionality and are further reacted with amino functional silane to produce self-crosslinking, ambient curing, film-forming polymers suitable for various uses including coatings and sealants for wood, glass and concrete.
U.S Patent Application No. 2008/0262192 describes water-soluble polymers having a high chelating performance and clay dispersancy that are suitable for use as detergents, water treatment agents and dispersants. These polymers are made by polymerizing an amino group-containing allyl monomer derived from adding an amine compound, such as iminodiacetic acid (IDA), to an allyl monomer, such as allyl glycidyl ether (AGE), with other polymerizable monomers including, without limitation, unsaturated monocarboxylic acid monomers.
Most recently, vinyl aminocarboxylate monomers have been found useful for providing amine-based chelating functionality. Vinyl aminocarboxylate monomers are an entire class of polymerizable acrylic monomers having amine-based chelating functionality and which are polymerizable along with ethylenically unsaturated monomers typically used to produce various types of acrylic monomers. This is related to the technology described in the aforementioned U.S Patent Application No. 2008/00262192 where an AGE-IDA vinyl aminocarboxylate monomer is described and incorporated into carboxylic acid-based copolymers. Polymers comprising polymerized units derived from such vinyl aminocarboxylate monomers have been identified as effective chelating agents and, therefore, are expected to be useful in various possible applications. U.S. Patent Application Publication No. 2013/0109823 (U.S. Ser. Nos. 61/553626, 61/553,642, 61/553,658) describe other vinyl aminocarboxylate monomers, including vinyl aminocarboxylate monomers produced from reactions between (IDA), iminodisuccinic acid (IDS), or salts thereof, and a vinyl epoxy benzene monomer, or between ethylenediamine triacetic acid (ED3A) or its salt, and polymerizable vinyl monomer such as vinyl epoxy benzene, allylglicidyl ether, or glycidyl(meth)acrylate, for example. Also disclosed are polymers having chelating functionality which comprise polymerized units derived from aminocarboxylate monomers produced from reactions between ethylenediamine disuccinic acid (EDDS), or its salt, and a polymerizable vinyl monomer such as vinyl epoxy benzene, allylglicidyl ether, or glycidyl(meth)acrylate. Thus, there has been a continuing need to improve the effective utilization of inorganic materials, such as titanium dioxide, in aqueous coating compositions and thereby to improve the opacity and other performance properties of coating compositions.
The present invention addresses the desire to maximize hiding efficiency of paint formulations containing inorganic materials, by providing aqueous dispersions of composite particles containing inorganic particles and polymeric latex particles, wherein the polymeric latex particles contain aminocarboxylic functional groups to promote adsorption of the polymeric latex particles on the surfaces of pigment surfaces. Specifically, the presence of the aminocarboxylic functional groups provides the latex with “chelant-like” capabilities, hence providing improved binding to inorganic materials in opaque coating formulations.